The construction of a cone of any given height or diameter is quite simple if the following method be observed. It is best to cut a pattern from a large piece of heavy paper, cardboard, or tin, Figure 3 illustrates the method of laying out a cone of the proper dimensions for the above trap. An ordinary square is placed on the material from which the pattern is to be cut; a distance (22 inches) equal to the height of the cone is laid off on one leg of the square at _A_, and a distance (9 inches) equal to one-half of the diameter of the base of the cone is laid off on the other leg at _B_, and a line is drawn between the points _A_ and _B_. With the distance between these points as a radius and with the point _A_ as a center, the portion of a circle, _C D_, is drawn. With a pair of dividers, the legs of which are set 1 inch apart, or with the square, lay off as many inches on the arc _C D_, starting at _C_, as there are inches around the base of the cone, which in this case is about 56½ inches, reaching nearly to the point _E_. Then add one-half inch for the lapping of the edges of the cone, and one-half inch which is taken up when the cone is tacked in, thus making a total distance from _C_ to _E_ of 57½ inches. Draw a line from _A_ to _C_ and another from _A_ to _E_, and cut out the pattern on these lines and on the arc from _C_ to as shown in figure 3. The edges _AC_ and _AE_ are then brought together, lapped one-half inch, and sewed with wire or soldered. After the aperture of the cone is formed by cutting off the apex, as previously described, it is ready for insertion in the trap. [Illustration: Fig. 3.--Method of laying out a pattern for the construction of a cone. Cut out on curved line _C_ to _E_ and on dotted lines from _A_ to _C_ and _A_ to _E_.] In order to figure the distance around the base of a cone of any given diameter multiply the diameter by 3.1416 or 3-1/7. The height of the legs of the trap, the height of the cone, and the size of the aperture in the top of the cone, each are of importance in securing the greatest efficiency. =OTHER FORMS OF CONICAL TRAPS.=